Resistivity structure of the central part of the Yamasaki fault studied bythe multiple electrodes resistivity method

The Yamasaki fault system is a well known major, active fault in South-West ern Japan. Large historical earthquakes have occurred along it. Several res istivity models of the Yamasaki fault have been proposed as the result of i ntensive electromagnetic investigations during the 1970's and 1980's. In 19 96, a trench study was made of the cross-section of the Yasutomi fault whic h is the kernel of the Yamasaki fault system. The cross-section showed the occurrence of past major paleo-earthquakes. To clarify the deeper structure of the fault, multiple electrode resistivity soundings were conducted acro ss the fault in 1997. Although the target sounding depth of the previous EM survey is different, the resistivity measurements show the boundary struct ure of the central part of the fault beneath the trench survey area. They a lso show the extent of a shallow conductive zone across the fault.